1. Field of the Invention
The invention relates to devices for supplying electrical power to X-ray tubes and more particularly, in such devices, it relates to connectors which are used for making electrical connections between the electrical power supply and the X-ray tube disposed in a tank filled with an insulating and cooling medium.
2. Description of the Prior Art
In diagnostic X-ray installations, the X-rays are generally produced by means of an X-ray tube. In one usual disposition, the X-ray tube is contained in a metal casing filled with an electrically insulating oil, with the casing being intended, in particular, to protect users against electric shock and against X-rays. The casing fitted with an X-ray tube is referred to as an X-ray source assembly. The components of the power supply for the X-ray tube and in particular the components of a high-voltage generator producing the high-voltage power supply for the X-ray tube are housed together in a different enclosure situated at a distance from the X-ray source assembly. Depending on the type of high-voltage power supply used, i.e. single pole or symmetrical, one or more highly-insulated electric cables convey the positive and negative polarities of the high voltage into the casing containing the X-ray tube via electrical connection devices. One such electrical connection device or connector is constituted by two portions, one of which, called the "receptacle" constitutes a female part which is permanently fixed on the casing, while the other portion constitutes a male part or "plug" which is intended to be received in the receptacle and which is fixed to the cable. Given the very high values that may be reached by the power supply voltage of an X-ray tube, e.g. 150 kV, the receptacle and the plug are made of electrically insulating materials and their shapes and sizes are defined by international standards. In order to protect users, the casing is connected to ground potential as is an outer sheath on the, or each, cable, with one of the perpetual concerns of manufacturers being that all the outside surfaces of the cables and of the casing of the connection device should be metallic and that there should be electrical continuity between all these members.
The electrical contact(s) provided by an electrical connection device occur in the bottom of the receptacle between first contact members fixed to the plug and second contact members fixed to the receptacle and passing through the bottom wall thereof, thus gaining access to the inside of the casing. The receptacle extends relatively deeply into the casing so that the end of the second contact element extends into the inside of the casing at a sufficient distance from the inside wall thereof to avoid electrical discharge between the metal casing which is grounded and the contact element which is at the high potential. Assuming that the polarity conveyed is negative, this contact is connected by a link conductor to the cathode of the X-ray tube, while the anode thereof is connected to the positive polarity via another link conductor inside the casing extending between the anode and another contact member of another electrical connection device.
However, on their own, these precautions are not sufficient for avoiding the risks of electrical discharges inside the casing and proper electrical insulation therein can be obtained only if the casing is filled with an electrically insulating oil or fluid. Under these conditions, it is impossible, in practice, in spite of the presence of an insulating oil, to place a metal component inside the casing close to the receptacle.
Depending on the type of X-ray tube used, the connectors have three or four connections which are spaced apart around a circumference having a diameter of 20.62 millimeters with the usual standards. For a three-connection connector, the connections are disposed at 120.degree. from one another. For a four-connection connector, a fourth connection is added on the same circumference halfway between two of the first three connections that are at 20.degree. intervals.
In new X-ray apparatuses, X-ray tubes are used which include, in addition to the cathode and the anode, electrodes referred to as "grids" or "gates" which serve to alter the path of the electron beam emitted by the cathode, or else to modulate it, or indeed to focus it better. The voltages applied to these gates may lie in the range several tens of volts to several kilovolts, and it is therefore necessary to provide power supplies for them via appropriate connectors.
Naturally, it would be possible to add another connector to the wall of the cooling tank in order to power supply these gates, however such a solution takes up space and increases the cost of the assembly.
The object of the present invention is therefore to provide a high-voltage X-ray tube connector having five connections, thereby power supplying the cathode, two cathode filaments, and two gates.